Bitter Espresso.
Good espresso should not be bitter, burnt or ashy. However, I seem to run across said espresso this week. After pulling numerous shots, drip, pour over and even a try at cupping, I can say without a shadow of doubt this coffee was a dud. It must have had a low quality Brazilian coffee in it that could not handle the darker roast that it was given.
Source: http://www.roaste.com/CoffeeBlogs/intrepid510/Bitter-Espresso